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A few thousand neutral grounding resistors could protect the United States from EMP

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H.R. 668, the Secure High-voltage Infrastructure for Electricity from Lethal Damage (or SHIELD) Act is a bill before congress which would require that the most critical components of America’s electrical infrastructure be secured against the threat posed by a potentially catastrophic electromagnetic pulse.

It has been proposed to add some fairly small and inexpensive resistors in the transformers’ ground connections. The addition of that little bit of resistance would significantly reduce the amount of the geomagnetically induced currents that flow into the grid. In its simplest form, it’s something that might be made out of cast iron or stainless steel, about the size of a washing machine. It is still at the conceptual design phase, but we think it’s do-able for $40,000 or less per resistor. That’s less than what you pay for insurance for a transformer.

GE sells neutral grounding resistors.

* NGRs are available from 480 volts to 72kv (line-line voltage).
* Initial Currents from 50 to 2,000A
* The standard NGR comes complete with an outdoor enclosure (galvanized or painted) for mounting on top of or next to a power transformer or generator.
* Numerous options are available ranging from CT’s, disconnect switches, elevating stands, stainless steel or aluminum enclosures, and grounding.

Space Review had some coverage of EMP hardening

The installation of supplemental transformer neutral ground resistors to reduce GIC flows is relatively inexpensive, has low engineering trade-offs, and can produce 60-70 percent reductions of GIC levels for storms of all sizes.

Other experts advocate improved cabling (e.g. industrial RS-485 cabling) in combination with improved external transient voltage suppressors to protect against the faster pulses. Specific methodologies for protecting against the lower priority fast EMP transients have been outlined in Cold War era (1984) NAS report “Evaluation of Methodologies for Estimating Vulnerability to Electromagnetic Pulse Effects”. Of course, protecting and hardening critical infrastructure from geomagnetic storms (and EMP) would also offer protection against some cyber-threats, sabotage, and natural disasters, like severe storms or hurricanes.

There has been some discussion that North Korea is developing a super-EMP nuclear device

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